#include <stdio.h>
/********found********/
double fun(int n)
{
    double s = 0.0;
    int a = 2;
    int b = 1;
    int c;
/********found********/
    for(int i=0;i<n;i++)
    {
        s = s + (double)a / b;
        c = a;
        a = a + b;
        b = c;
    }
    return s;
}
void main() {
    int n;
    scanf_s("%d", &n);
    printf("%lf\n", fun(n));
}
